I have two identical PCs running Vista. Since yesterday, the buttons on the YouTube website do not work in Internet Explorer 8 on one machine only. I am also getting "Errors on page" messages in the status bar, the Upload page not fully loading, and the message "Hello, you either have JavaScript turned off or an old version of Adobe's Flash Player" on some channel pages, although as far as I can tell, I have the latest versions of Flash (10.1.85.3) and Java (6.22), and JavaScript works on a test site, and I have not changed any settings. I checked for Windows updates, cleared the browser cache, and tried running IE without add-ons, but it still doesn't work.

My first hunch was that the problem was something to do with YouTube, but that works in IE8 on my other PC, and it works in Firefox on this one; i.e., the problem is only on one machine and only in IE8 and only on YouTube. What could be causing this?